In power stations cooled by fresh water, the industrial water is discharged via a gravity-fed basin into a receiving body of water for operating reasons. A receiving body of water is stationery or flowing water into which the industrial water is discharged. The gravity-fed basin consists mainly of a water basin with a sill over which the industrial water is discharged into the receiving body of water. The industrial water is discharged into the receiving body of water only when the water level exceeds the height of the sill. The sill can be designed either as a linear sill or, for example, be formed by the top edge of a gravity cylinder extending upwards from the bottom of the water basin, such as is, for example, described in DE 31 03 306. The gravity cylinder described in DE 31 03 306 also has means for increasing the air input into the industrial water.
Depending on the type of power station, the throughput of industrial water through the gravity-fed basin is approximately 5 to 10 m3 per second depending on the permitted heating span of the industrial water. Depending on fluctuations in the water level of the receiving body of water, the industrial water flowing over the sill drops a few meters into the depth in order to mix with the water of the receiving body of water. Even if no measures are taken to introduce air into the industrial water, a high air input takes place as the water drops into the depth, which leads to more or less severe foaming depending on the water quality. This air input or foaming is usually unwanted either by the authorities or by adjoining owners.
Therefore, measures are usually tried and tested during the commissioning of a gravity-fed basin to reduce the air input or foaming. Such measures can sometimes be temporary covers that include the injection of chemicals, or ventilating or pipe systems. The latter in particular can lead to enormous additional costs.
Furthermore, the gravity-fed basin sometimes requires a relatively large building area.